Make Magic::new accept an array of paths from which to load the Magic database.

Signed-off-by: Krzysztof Wilczynski <krzysztof.wilczynski@linux.com>
Make Magic#check and Magic#compile work correctly even when no argument is given.

Signed-off-by: Krzysztof Wilczynski <krzysztof.wilczynski@linux.com>